Methods of counteracting gravitational forces on the human body have been devised for therapeutic applications as well as physical training. Rehabilitation from orthopedic injuries or neurological conditions often benefits from precision unweighting (i.e., partial weight bearing) therapy. One way to counteract the effects of gravity is to suspend a person using a body harness in conjunction with inelastic cords or straps to reduce ground impact forces. However, currently available harness systems are often uncomfortable and require suspension devices or systems that lift the user from above the user's torso.
Many other existing unweighting systems are simple affairs, often relying on stretched bungee cords to provide unweighting forces. However, many of the systems suffer from an inability to easily adjust or control unweighting force. Further, many of the systems rely on inelastic overhead cables that supply minimal vertical compliance.
Differential Air Pressure (DAP) systems have been developed to use air pressure in a sealed chamber enclosing the lower portion of the user's body to simulate a low gravity effect and support a patient without the discomfort of harness systems or the inconvenience of other therapies. While highly controllable and reliable, some DAP systems have an operating envelope and degree of complexity that make them better suited to environments where assistance is readily available.
In view of the above shortcomings and complications in the existing unweighting systems, there remains a need for simple yet effective unweighting systems. In particular, for an average user who may not have a medical condition warranting physical therapy or medical supervision, there is also an additional need for unweighting systems suited to gym or home use. As such, a need exists for an unweighting system that allows users economical and effective alternatives to the current techniques available.
An important characteristic of unweighting systems intended for exercise or gait training is a low vertical spring rate, where the user's vertical position has minimal influence on the unweighting force applied to the user. This is significant because as a user walks or runs, their vertical displacement during different phases of the gait cycle can vary by +/−two inches or more. A low vertical spring rate ensures that the unweighting force is nearly equal during all phases of the gait cycle. While fluid based systems such as DAP or pool-based therapies have inherently low vertical spring rates, the same is not true for most mechanical unweighting systems. The need for a low spring rate often requires the use of very long spring elements such as bungee cords, making these systems less than compact and/or unable to exert more than minimal unweighting forces. A further need is for a compact unweighting system with a low vertical spring rate.